The subject matter disclosed herein relates to a recloser device for an electrical distribution system and in particular to a recloser device that can determine the presence of an electrical fault prior to closing.
Electrical utilities have a number of metrics that are used to track performance and customer satisfaction. These metrics, which include the system average interruption frequency index (“SAIFI”), the customer average interruption duration index (“CAIDI”), and for some utilities, the momentary average interruption frequency index (“MAIFI”). SAIFI measures the average number of interruptions that a customer would experience during a time period, such as a year. CAIDI measures the duration of the interruption that a customer would experience, and is generally a few hours per year. MAIFI measures the number of power interruptions that have a duration of less than five minutes that a customer would experience during a given time period.
Some or all of these metrics are also used by government regulators to aid in determining if the electrical utility is adhering to the regulations in maintaining a durable and reliable electrical distribution network. As a result, electrical utility and distribution companies have developed system architectures that minimize the duration and frequency of power outages. One technique uses a device called an “autorecloser” or simply “recloser”, in the protection scheme for the distribution system. A recloser is a type of circuit breaker that includes a mechanism that allows the circuit breaker to close or reconnect the electric circuit after an electrical fault is detected. The premise of the recloser is that many electrical faults on the overhead open wire system are transitory, due to issues such as a tree limb touching or falling on a power line for example. The recloser includes a controller that is programmed to make several attempts to reconnect before locking open the recloser. Generally, the feeder recloser is programmed with an operating profile that provides for one “fast” trip and one to three “slow” trips before finally locking open.
Another technique used to improve performance is to arrange the electrical circuits in what is commonly referred to as an autoloop system. In an autoloop, the distribution network is divided into two or more branch circuits that can be adaptively coupled in the event of a failure. Generally, a substation will provide two or more feeder branch circuits to a typical autoloop. A feeder recloser is positioned at the beginning of the circuit and provides the protection functionality discussed above. A second recloser is positioned at an intermediate position along the branch circuit. The second recloser may be a “midpoint” type recloser that opens in response to a downstream fault. In addition or in place of the midpoint recloser, the system may include a sectionalizing recloser that opens in response to a downstream fault or may open in response to a loss of voltage. Positioned at the end of the branch circuit is a third type of recloser known as a “tie” recloser. The tie recloser couples the branch circuit with a similarly configured adjacent branch circuit. A sectionalizing recloser is different from a tie recloser in that a sectionalizing recloser will open in response to a fault that occurs downstream under normal current flow condition. A sectionalizing recloser will also open after a predetermined amount of time following a loss of voltage.
The tie recloser is normally in an open position to prevent the flow of electrical current between the branch circuits. In the event of a fault between the feeder and midpoint that the feeder recloser cannot clear, the feeder recloser locks open and results in a loss of potential on the entire branch circuit. When this occurs, the midpoint recloser changes settings to trip/open at a lower current level and lock open after only one trip. The tie recloser is arranged to automatically close at short period of time, typically 15 to 100 seconds, upon the detection of the loss of voltage potential. When the tie recloser connects the two branch circuits, electrical current can flow into the branch circuit with the electrical fault. Depending on where the fault is located on the branch circuit, partial electrical service can be restored to the portion of the branch circuit that experienced the failure. For example, if the fault occurs between the feeder recloser and the midpoint recloser, when the tie recloser connects the circuits, electrical power flows into the branch circuit. Since the fault is still present, the midpoint recloser trips and locks open. However, electrical power is still available for the customers between the sectionalizer/midpoint recloser and the tie recloser. Thus the average duration of electrical power loss and the amount of affected customers are minimized.
It should be appreciated that when the recloser closes to flow electrical power into the adjacent branch circuit, if there is a fault in the segment of the branch circuit between the recloser and the next fault protection device that the recloser will experience a fault condition. In some circumstances, the recloser may not react fast enough and an upstream protection device (such as a circuit breaker in the substation) may trip causing a loss of power in the circuit up to the point of the recloser. It should be appreciated that it is desirable to avoid closing a recloser device into an electrical fault.
Accordingly, while existing recloser devices are suitable for their intended purposes the need for improvement remains, particularly in determining if fault is present in an adjacent electrical network circuit segment.